This application claims the priority of German patent document PA 19715810, filed Apr. 16, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a data bus for a vehicle having a plurality of subscribers which operate through peripheral S/E modules and an optical transmission line on a central bus, which has associated S/E modules which are connected to one another.
In a data bus of this kind, the peripheral S/E modules may emit a continuous light signal due to an external influence such as an accident, or due to an internal error. However, the S/E bus modules possess a low level of intelligence, merely converting the light signal entering from the peripheral module into a corresponding electrical or optical control signal, passing it on to the other bus modules. Therefore, such an anomaly results in a complete blockage of the data bus, in which all of the bus modules receive a continuous control signal. Since the bus modules and the peripheral modules do not differ from one another in their basic design, they shut off the input connected to the corresponding bus module, and the bus is then no longer operable.
The object of the invention is to provide a data bus of the type recited at the outset that remains operable at least to a limited degree in case of error.
This and other objects and advantages are achieved by the bus arrangement according to the invention, which monitors light signals transmitted via the bus, and when an S/E bus module receives a light signal which is longer than a maximum permissible signal length, the respective S/E bus module shuts off the corresponding peripheral S/E module. The entire data bus, except for this peripheral S/E module, then remains operable.
Since the S/E bus modules, as stated above, pass the incoming continuous light signal to their peripheral S/E modules as a continuous light signal, it may happen, due to component tolerances, that a peripheral S/E module that is intact shuts off before the source of the problem (a defective peripheral S/E module) can be shut off by the associated bus module. In order to restore the operability of the bus at least to the extent possible in this case, (that is, to shut off permanently only the defective peripheral S/E module), a routine for switching the intact peripheral S/E modules on again can be provided.
For this purpose, a bus master can be provided within the bus system which emits synchronization pulses at regular intervals. (The function of the bus master may be performed by a separate component or by an S/E bus module, for example.) The defective peripheral S/E module remains shut off for as long as it continues to emit a continuous light signal, while the other S/E modules are switched on again when they receive a synchronization pulse.
In this case, neither a light signal nor a control signal is applied for a time that is longer than the maximum permissible signal length. This activation can also be triggered automatically by internal logic provided in the S/E bus module. Operation can thus be resumed when the problem in the S/E module itself has been corrected and the module no longer emits a continuous light signal, or when the problem in another S/E module has been eliminated and a corresponding S/E bus module no longer receives a continuous control signal. In this way, assurance is provided that the bus is reactivated at least to the extent possible. This reactivation is always limited to the ranges that are functional.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.